Prevention of decomposition of halogenated hydrocarbon solvents



United States Patent O PREVENTION OF DECOMPOSITION OF HALO- GENATED HYDROCARBON SOLVEN'IS Leighton S. McDonald, Freeport, Harris G. Hughes, Angleton, and Clarence R. Crabb, Lake Jackson, Tex.,

assignors to The Mich., a corporation of Delaware No Drawing. Application August 1, 1958 Serial No..752,416

4 Claims. (Cl. 260-6525) .This invention relates to the prevention of decomposistances, which render the solvent unsuitable forsuch purpose as metal vapor degreasiug, dry cleaning'and oil extracting. It is also known that whenthehalogenated hydrocarbons are exposed to 'excess'ivexheat, they decompose by a condensation-type reaction to form jhydrochloric acid together with a resinous material. In the presence of many metals, for example, iron, aluminum, zinc, copper or the aluminum-base metals, the hydrochloric acid thus formed reacts with these metals to form the chloride salts which act as catalysts for the condensation reaction. Thus, when this condensation reaction takes place in metal vapor degreasing where the chips of these metals are in contact with the boiling halogenated hydrocarbon solvents, the reaction, i.e., decomposition, often becomes autocatalytic. When this occurs, the solvent decomposes very vigorously with the evolution of large quantities of hydrochloric acid and the formation of a tarry or gummy mass in the solvent.

As the major applications of the chlorohydrocarbon solvents involve cyclic processes in which the solvent is recovered by distillation, the solvent should be protected with an inhibitor which is recovered with the solvent on distillation. For this same reason, the inhibitor used should not react with free fatty acids, a common contaminant in solvent applications. For example, in metal vapor-degreasing, bufling compounds and drawing oils are sources of fatty acid. Bufiing compounds generally contain about 50 percent of stearic acid while drawing oils contain as much as 5 to percent of oleic acid.

An object of this invention is to provide a stabilizer for chlorohydrocarbons, such as trichloroethylene and perchloroethylene, which will inhibit the tion decomposition reactions. Another object of this invention is to provide a stabilizer for trichloroethylene which will inhibit the condensation type decomposition reaction which is catalyzed by the presence of light, heat or oxygen. Still another object of this invention is to provide a stabilizer for trichloroethylene or perchlor0 ethylene which can be readily recovered with the solvent and which need only be present in relatively small concentrations, usually a small fraction of one percent.

Dow Chemical Company, Midland,

light and heat normal oxida- 2,917,555 Patented Dec. 15, 1959 The chlorohydrocarbons, such as trichloroethylene, perchloroethylene, and the like, when stabilized with pyrroles in the manner of U.S. Patent 2,492,048; the oximes in the manner of U.S. Patent 2,371,646; the alkylamines as described in British Patent 391,156; or the S-membered N- and S-heterocyclic compounds of U.S. Patent 2,517,893; are not lastingly stable under the severe conditions of present-day-industrial users where strong light, oxygen and heat are encountered. The solutions are gradually depleted of stabilizer and are thus subject to decomposition and ultimately attach the materials being cleaned and/ or containing the solvents.

It has now been found that chlorohydrocarbons such as trichloroethylene, perchloroethylene and the like, containing any one or more of the above mentioned stabilizers are materially improved in its ability to resist decomposition by light, heat and/or oxygen when an amine borane or an ammonium salt of borane or an alkyl-substituted borane is added to the already inhibited solvent. Thus if one adds from 0.001 percent by weight to 1.0 percent by weight of a borane compound,,th,e solvent is stabilized against decomposition or polymerization even-under severe conditions heat.

Borane compounds and preferably those boranes having the general formula wherein each R is lower alkyl or hydrogen and each R is alkyl or hydrogen but at least one R is hydrogen, are operable in accordance with the present invention. Following are examples of the boranes suitable as stabilizers according to the present invention: dimethylamine borane, trimethylamine borane, isopropylamine borane, methylamine methyl borane, dimethylamine methyl borane, trimethylamine methyl "borane, dimethylamine borane, and ammonium borane.

The following examples illustrate the present invention but are not to be construed as limiting.

Examples 1-12 Tests were conducted employing various inhibitors and stabilizers on ZOO-milliliter samples of trichloroethylene or perchloroethylene in which a strip of SAE 1010 steel was suspended. A second strip of the same type steel was suspended above the liquid to be in the vapor phase. An oxygen delivery tube was suspended to introduce oxygen into the liquid near the bottom of the flask containing the trichloroethylene. The rate of introduction was adjusted to introduce l0-l2 bubbles per minute. A ISO-watt electric light bulb was placed under the flask to provide heat and light to the system. The test was conducted for 48 hours at the reflux temperature and then the acidity of the solution measured as percent HCl.

employing the various stabilizers as indicated.

of light, oxygen and/or mature Example Iei'eent Percent Appearance alter No. Percent of Additive HClAiter HClMter 48 Hrs. Acceler- 48 Hrs 24 Hrs. ated Oxidation .025 N-methylpyrrole .025 N-methylpyrrole+.005 dimcthylarnine borane .025 N-methylpyrrole+.0010 dimethylarnlne borano Dark amber. Medium amber. Water white. Heavy black .025 pyrr .025 pyrrole+.0015 dlmethylnmine borane 6 .025 pyrrole+.0030 dlmethylamine borane 7- .0025 N-motiylpyrrole 8. .0025 N'rnetbylpyrrole+.002 dimethylarulne borane... 9. .0020 dimethylarnine borane .001 dimethylamine borane. No stabilizer (control) rane.

ppt. solution opaque. Water white.

Amber: Water white.

Examples. 18-21 In the manner of the foregoing examplesemploying perchloroethylene in place of trichloroethylene there was obtained the following results after 24 hours.

1. A stabilized chlorinated hydrocarbon solvent comprising from 0.001 to 1.0 percent by weight of a member selected from the group consisting of unsubstituted and alkyl-substitutcd pyrroles, 'N-lower alkyl substituted pyrroles, pyridine, a-picoline, oximes, isoxazolines, thiazole, thiazolines, lower alkylamines, unsubstituted and lower..alky1-substituted'arylamines and diazinesand from 0.0011011!) percent by weight of =21 member having the formula:

wherein each R and R are independently selected from the groupconsisting of hydrogen and lower alkyl and at least one 'R', is hydrogen.

'2. A mixture comprising trichloroethylene, from 0.001 to :110- percent by -weight of N-methylpyrrole and from .000l.:to'1"t0=percent by weight of 'dimethylamine-borane.

.BWA :mixture :comprising -of trichloroethylene, from 0.001 to. 11.0 percentby'weight of pyrrole and from .0001 to l:.0 ;.percent by" weight of dimethylamine-borane.

4. :AIIDiXU-XI'CIODJPIiSiHg trichloroethylene, from 0.001 to 115.0 percent by'weight of'pyridine' and'from .0001 to 1 lLQWntibyF-Weight of :dime'thylami'ne-borane.

.Referencesfiited in the file of this patent .Starks June 11, .1957 

1. A STABILIZED CHLORINATED HYDROCARBON SOLVENT COMPRISING FROM 0.001 TO 1.0 PERCENT BY WEIGHT OF A MEMBER SELECTED FROM THE GROUP CONSISTING OF UNSUBSTITUTED AND ALKYL-SUBSTITUTED PYRROLES, N-LOWER ALKYL SUBSTITUTED PYRROLES, PYRIDINE, A-PICOLINE, OXIMES, ISOXAZOLINES, THIAZOLE, THIAZOLINES, LOWER ALKYLAMINES, UNSUBSTITUTED AND LOWER ALKYL-SUBSTITUTED ARYLAMINES AND DIAZINES AND FROM 0.001 TO 1.0 PERCENT BY WEIGHT OF A MEMBER HAVING THE FORMULA: 